1. Field of the Invention
The present invention relates to a method of manufacturing a 2-5 inch diameter glass substrate for a magnetic disc by pressing a disk-shaped plate glass, and particularly to a method of manufacturing such a glass substrate for use in computers to store such digital data as audio and video data and graphics data, as well as in setup boxes.
2. Description of the Related Art
Conventionally, polycarbonate, acrylic, epoxy, olefin, and other resinous materials have been used as the base material for magnetic discs and the like. However, these materials can be affected by high temperature, humidity, and other environmental conditions and can deteriorate over time. Discs composed of these materials are also restricted in storage capacity. Accordingly, glass, which is not affected by high temperatures, has been incorporated as a base material for magnetic discs and the like.
A glass substrate is formed from a plate glass molded through a fusion or float method. After being inspected, the plate glass is cut into a prescribed disc-shape and annealed at a temperature of 300-500.degree. C. After the annealing process, a peripheral process and polishing process are performed to provide a flat finish on the surfaces and edges of the disc.
Recently, a method already used in such optical systems as the manufacturing of lenses with small apertures has been employed in the manufacturing of glass substrates for magnetic discs. This method uses a metal mold having a precisely formed surface to press mold glass that has been preformed through cutting, annealing, and other processes in order to obtain a product having a prescribed flatness. Here, the metallic mold is formed of a super-hard material that is coated with a graphite or amorphous diamond-like carbon coating to achieve a precise smoothness. The carbon coating is applied to the surface to cover cavities formed therein. Without coating the surface of the mold, these cavities will transfer flaws to the surface of the molded glass.
However, in the conventional method of manufacturing a glass substrate for a magnetic disk, a lapping process is required to adjust the thickness and outer edge of the press molded product. Much time and effort is required to perform this polishing process. After the polishing process, the molded glass substrate is washed with an organic neutralizer and pure water. Accordingly, such a process requires expensive equipment to supply the neutralizer and pure water and to perform a post-process on the resulting wastewater. After about ten thousand continuous shots, the carbon coating begins to peel from the surface of the mold used to form the glass substrate.
Therefore, the inventors of the present invention performed ion implantation in the surface of the mold member formed of a super-hard material and having a prescribed smoothness in order to improve the material's resistance to friction, abrasion, and fatigue. This ion implantation also improved the adhesiveness of the carbon coating on the surface of the metallic mold member, greatly improving the life of the mold. By using such a mold, it is possible to press mold a plate glass to obtain a molded product with few errors in diameter and thickness. This mold also enables the manufacturing of 2-5 inch diameter glass substrates for magnetic discs, while rendering the lapping process unnecessary and reducing the overall time of the manufacturing process.